The present invention relates to an eccentric oscillating-type speed reducer for effecting speed reduction by eccentrically rotating pinions.
The present applicant proposed in Japanese Patent Application No. 2000-202030 an eccentric oscillating-type speed reducer which makes it possible to make the manufacturing cost low and make the assembling operation simple by forming a plurality of pinions by pinions of the same shape.
This eccentric oscillating-type speed reducer is comprised of an outer casing having internal teeth formed on its inner periphery; a plurality of pinions which are accommodated in the outer casing, which have on their outer peripheries external teeth meshing with the internal teeth, the number of the external teeth being slightly smaller than that of the internal teeth, and which are juxtaposed in parallel in an axial direction; an even number of not less than four crankshafts which are arranged in such a manner as to be spaced apart from each other at equal angles in a circumferential direction, central portions of the crankshafts being inserted in the pinions, so as to eccentrically rotate the pinions as the crankshafts rotate; a carrier which is inserted in the outer casing for rotatably supporting both end portions of the crankshafts; an input shaft supported rotatably by the outer casing and having a driving external gear coaxial with the internal teeth; and driven external gears respectively mounted on the crankshafts and meshing with the driving external gear while surrounding the driving external gear.
However, in the case where the number of the crankshafts is thus set to an even number of not less than four, if an attempt is made to enlarge the speed reduction ratio of the eccentric oscillating-type speed reducer by making the diameter of the driving external gear small while making the diameter of each driven external gear large, the adjacent driven external gears come to interfere with each other at a point of time when the diameter of each driven external gear has not yet been made very large. Consequently, there has been a problem in that the reduction ratio based on the driving and driven external gears cannot be made very large. For example, in a case where the number of crankshafts is four, the reduction ratio based on the driving and driven external gears has been 2.1 at maximum.
The object of the invention is to provide an eccentric oscillating-type speed reducer which makes it possible to make a final speed reduction ratio and a final output torque substantially large by enlarging the reduction ratio based on the driving and driven external gears.
The above object can be attained by an eccentric oscillating-type speed reducer including an outer casing having internal teeth formed on an inner periphery thereof; a plurality of pinions which are accommodated in the outer casing, which have on outer peripheries thereof external teeth meshing with the internal teeth, the number of the external teeth being slightly smaller than that of the internal teeth, and which are juxtaposed in parallel in an axial direction; an even number of not less than four crankshafts which are arranged in such a manner as to be spaced apart from each other at equal angles in a circumferential direction, central portions of the crankshafts being inserted in the pinions, so as to eccentrically rotate the pinions as the crankshafts rotate; a carrier which is inserted in the outer casing for rotatably supporting both end portions of the crankshafts; an input shaft supported rotatably by the outer casing and having a driving external gear coaxial with the internal teeth; and driven external gears respectively mounted on the crankshafts and meshing with the driving external gear while surrounding the driving external gear, the eccentric oscillating-type speed reducer characterized in that
the driven external gears are classified into a plurality of paired-gear groups each consisting of two driven external gears spaced apart from each other by 180 degrees in the circumferential direction, axial positions of the two driven external gears making up each of the paired-gear groups with respect to the input shaft are made identical, and a different paired-gear group is arranged by being offset in the axial direction of the input shaft.
In this invention, as described above, the driven external gears are classified into a plurality of paired-gear groups each consisting of two driven external gears spaced apart from each other by 180 degrees in the circumferential direction, axial positions of the two driven external gears making up each of the paired-gear groups with respect to the input shaft are made identical, and a different paired-gear group is arranged by being offset in the axial direction of the input shaft. Therefore, only two driven external gears making up the paired-gear group are present at an identical axial position of the input shaft. Consequently, even if the diameters of these driven external gears are made large up to the very limit, these driven external gears do not interfere with each other. Accordingly, it is possible to readily enlarge the reduction ratio based on the driving and driven external gears, with the result that it is possible to substantially enlarge the final reduction ratio without lowering the final output torque in the eccentric oscillating-type speed reducer.
In addition, since the space formed between the bottom of each of the prepared holes and the tip of each of the bolts is located not in the column portion but in the base portion, the entire column portion assumes a solid structure, thereby increasing the strength and permitting the output of high torque.
In addition, the bearing and the seal member interposed between the outer casing and the input shaft can be lubricated by the lubricating oil filled in the sealed space, so that a lubricating device for lubricating the bearing and the seal member or the operation for replenishing the lubricating oil are made unnecessary.
In addition, even if the lubricating oil in the sealed space expands due to the temperature rise of the speed reducer, this expansion is absorbed by the compression of the air in the air reservoir, so that the leakage of the lubricating oil can be prevented.
The present disclosure relates to the subject matter contained in Japanese patent application No. 2001-277509 (filed on Sep. 13, 2002), which is expressly incorporated herein by reference in its entirety.